1. Field of the Inventions
The present inventions relate to a catalyst support, and methods of producing the same, having porous alumina formed with pores within which magneto-plumbite type complex oxide ((La.M)Al11O19 (where M is Mn or Fe)) is formed and a noble metal is supported on the magneto-plumbite type complex oxide, and also relates to a catalyst, a catalyst support, and manufacturing methods thereof, including porous alumina formed with pores within which magneto-plumbite type complex oxide (La(Mnx.M1-x)Al11O19 (where M is Co, Cu or Nb)) is formed and a noble metal is supported on the magneto-plumbite type complex oxide.
2. Description of the Related Art
Generally, it is believed that the performance of an emission purifying catalyst may deteriorate as a result of the growth of micro particles of noble metal functioning as catalyst activating components. The micro particles of noble metal are generally distributed on a surface of heat resistant alumina support (catalyst support). However, because these micro particles grow via aggregation after being repeatedly distributed on the alumina surface in accordance with increase of circumference temperature, various technologies have been developed to prevent deterioration of performance of the noble metal catalyst by suppressing the movement or distribution of the noble metal particles on the catalyst surface.
For example, Japanese Laid-open Patent Publication No. 135963/2003 discloses a method for suppressing the movement or distribution of micro particles of noble metal by confining them within pores of an alumina catalyst support. In such a method, it is proposed to prevent aggregation of noble metal particles in pores of the alumina catalyst support by confining oxide particles such as cerium oxide, zirconium oxide, or magnesium oxide simultaneously with the noble metal particles.
Recently, a perovskite-type complex oxide catalyst having a good heat resistance has been disclosed. The perovskite-type complex oxide is usually described as “ABO3” and, in many cases, lanthanum (La) is used as “A” and iron (Fe), cobalt (Co) or manganese (Mn) is used as “B”. Although the perovskite type complex oxide catalysts, such as LaFeO3, LaCoO3, and LaMnO3 have emission purifying activity by simply using them, it has been pointed out that they can not treat a sufficient amount of emission and that they are insufficient in NO purifying ability. To overcome these faults, LaFe(1-x)PdxO3 has been proposed, which is obtained by replacing part of Fe ions in LaFeO3 with a noble metal (Pd) ions (see Japanese Laid-open Patent Publication No. 31367/1993).
On the other hand, it has been proposed to use, as a catalyst, a magneto-plumbite type complex oxide formed by alumina as its primary ingredient and containing lanthanum (La) as an alkaline earth metal and also proposed in this case to select manganese or iron as a metal atom to be replaced with Al in magneto-plumbite complex. It is supposed that the magneto-plumbite-type complex oxide (hereinafter described as “MPB”) has the heat resistance superior to that of the perovskite type complex oxide and it forms a crystal lattice having alumina (Al2O3) or iron oxide (Fe2O3) as its primary ingredient and contains alkali metal ions or alkaline earth metal ions within the crystal lattice.
Another technology has been proposed to produce an emission purifying catalyst having a good heat resistance by dipping an MPB described as AMnxAl(12-x)O19 (where A is an alkali metal, an alkaline earth metal or a rare metal) into aqueous solution of noble metallic salt (see Japanese Laid-open Patent Publication No. 271672/1997). According to this prior art, the emission purifying catalyst can be obtained by exactly weighing one molar La2O3, one molar Mn2O3 and 11 molar Al2O3 precursor to synthesize an Mn replaced MPB ((La.Mn)Al11O19.x) and then by burning it at a temperature higher than 1300° C., preferably at 1450° C. for 5 hours or more.